1. Field of the Invention
The present invention relates to a semiconductor device and a method of forming the same. More specifically, the present invention is directed to a capacitor having a reaction preventing layer and methods of forming the same.
2. Description of Related Art
Capacitors enjoy widespread use in various semiconductor device applications, due to their charge-storing capabilities. Representative semiconductor devices that employ capacitors are DRAM devices. A unit cell of a DRAM device uses a capacitor as a data storage element. With the continued trend toward more highly integrated semiconductor devices, much effort has been applied to increasing the capacitance of a capacitor within a limited area.
A typical approach for increasing the capacitance of a capacitor is to increase an overlap area of both electrodes of a capacitor within a limited area. Therefore, very tall cylindrical lower electrodes have been suggested. However, as semiconductor devices become increasingly scaled down, methods for increasing the height of a cylindrical lower electrode result in the introduction of many problems, for example, inclination of the lower electrode or a high step difference between a peripheral circuit area and a cell area.
Another method for increasing the capacitance of a capacitor is to form a higher-k dielectric film as the dielectric substance of a capacitor. The higher the dielectric constant of the dielectric substance, the more the capacitance of the resulting capacitor increases. Unfortunately, a capacitor having a high-k dielectric film may encounter certain limitations. That is, a lower electrode made of polysilicon may become oxidized. If the lower electrode of polysilicon is oxidized, a silicon oxide layer of a low-k dielectric constant may be formed, which can result in a decrease in capacitance. Since a silicon oxide layer is vulnerable to leakage current, the leakage current characteristics of a capacitor may be degraded. For this reason, a technique for forming a reaction preventing layer between a lower electrode and a high-k dielectric film has been suggested for preventing reaction therebetween.
A reaction preventing layer comprising nitride is disclosed in Korean Patent Application No. 2002-13189. According to Korean Patent Application No. 2002-13189, a nitride layer is formed on a lower electrode using atomic layer deposition (ALD) to prevent a reaction from occurring between an applied dielectric film and the lower electrode. The nitride layer comprises, for example, aluminum silicon nitride (AlSiN).
However, if an aluminum silicon nitride layer is formed using ALD, characteristics of a capacitor may be degraded. Conventionally, ALD is carried out at a low temperature of 300-500 degrees centigrade. In this regard, source gases for forming an aluminum silicon nitride layer must have a sufficient reactivity at the low temperature. But it is uncommon for silicon source gases to have sufficient reactivity at low temperature.
In one approach, the use of a catalyst was suggested as a way to enable silicon source gases to have sufficient reactivity at low temperature. In this approach, a silicon precursor of halogen silicon compound and a catalyst such as amine are introduced into a chamber to secure a silicon source having sufficient reactivity. However, byproducts of the amine catalyst, particularly, carbon substance in the amine, may come to reside in the aluminum silicon nitride layer, which can degrade layer characteristics. As a result, leakage current of the resulting capacitor may increase. This, in turn, can result in degradation of various electrical properties of the resulting capacitor.